Iraqi security forces have fired tear gas and live bullets at protesters who stormed into Baghdad's heavily fortified Green Zone.

The incident on May 20, involving thousands of demonstrators who gathered outside of the Green Zone's security check points before storming the district, prompted Prime Minister Haider al-Abadi to declare a curfew in Baghdad.

Some protesters also overwhelmed security forces to enter Abadi's office.

Journalists at the scene reported seeing dozens of demonstrators with injuries, including one man who was shot in the head.

The demonstrators included supporters of the powerful Shi'ite Muslim cleric Moqtada al-Sadr and people from other groups who are angry about the government's failure to approve anticorruption reforms and improve security.

Later on May 20, Sadr issued a statement in support of the protesters and condemning the use of force against them by security forces.

Addressed to the demonstrators, Sadr's statement said: "I respect your choice and your peaceful spontaneous revolt. Curse the government that kills its children in cold blood."

The protest followed a demonstration on April 30 where demonstrators also stormed into the Green Zone -- a district that includes the parliament, government buildings, and many foreign embassies.

In February, Abadi revealed plans to appoint a government of independent technocrats to uproot a system of political patronage that contributes to corruption.

Sadr supports Abadi's plan.

But the cabinet reshuffle is opposed by Iraq's most powerful Shi'ite militias -- the Saraya al-Khorasani Brigade and the Badr Organization -- which receive funds, weapons, and training from Iran.

That puts them at odds with Sadr, who was once supported by Iran but recently has positioned himself as more of a nationalist leader in Iraq.

Khorasani fighters, Badr militia, and Sadr's so-called Peace Brigades are all part of an umbrella group known as Hashid Shaabi, or Popular Mobilization Forces.

They have been fighting alongside the U.S.-backed Iraqi army against Islamic State (IS) militants.

But their unity appears to be fraying, raising concerns about the ability of Iraqi forces to fight against IS extremists.

Since last week, politicians from the blocs of Badr and Sadr have accused each other of complicity in recent bombings claimed by Islamic State.